Enhanced photo-fermentative hydrogen production by constructing Rhodobacter capsulatus-ZnO/ZnS hybrid system

This study incorporated ZnO/ZnS nanoparticles with Rhodobacter capsulatus SB1003, forming a hybrid system to promote photo-fermentative hydrogen production. The results indicate that the material's photocatalytic activity and concentration significantly affected hydrogen yield. The addition of ZnO/ZnS exhibited a more significant auxiliary effect than ZnO and achieved an approximately 30% increase in hydrogen production compared to the control group. ZnO/ZnS enhanced the production of extracellular polymers, thereby strengthening the synergy between the nanomaterials and the bacteria. The photogenerated electrons from ZnO/ZnS were utilized by the photosynthetic bacteria. Furthermore, the activity of nitrogenase was enhanced, resulting in improved hydrogen production performance. This study provides insights into hydrogen production by photosynthetic bacteria with the assistance of inorganic semiconductor nanomaterials.

Photofermentative biohydrogen generation from organic acids by Rhodobacter sphaeroides O.U.001: Computational fluid dynamics modeling of hydrodynamics and temperature

Hydrogen gas is a clean-burning fuel suitable for powering public vehicles. Hydrogen fuel has the highest energy density (143 MJ kg^-1 ). This research paper emphasizes three-dimensional hydrodynamics and temperature distribution during photobiohydrogen generation by Rhodobacter sphaeroides strain O.U.001 in a triple-jacketed 1 L photobioreactor (PBR). The fermentation broth has turbulent flow conditions and light gradients among various layers, which affect the light conversion efficiency of the PBR. From the carbon source (malic acid), various organic acids are produced within fermentation (lactate, acetate, and formate). Modeling and simulation studies by computational fluid dynamics confirmed uniform fluid dynamics and heat transfer throughout the annular PBR. The modified Gompertz equation gave good simulated fitting with an experimental value for H₂ generation. R. sphaeroides O.U. 001 gave good simulated results for H₂ generation with mathematical modeling of substrate consumption kinetics and substrate utilization for biomass.

Improved O2-tolerance in variants of a H2-evolving [NiFe]-hydrogenase from Klebsiella oxytoca HP1

In this study, we investigated the mechanism of O2 tolerance of Klebsiella oxytoca HP1 H2-evolving hydrogenase 3 (KHyd3) by mutational analysis and three-dimensional structure modeling. Results revealed that certain surface amino acid residues of KHyd3 large subunit, in particular those at the outer entrance of the gas channel, have a visible effect on its oxygen tolerance. Additionally, solution pH, immobilization and O2 partial pressure also affect KHyd3 O2-tolerance to some extent. We propose that the extent of KHyd3 O2-tolerance is determined by a balance between the rate of O2 access to the active center through gas channels and the deoxidation rate of the oxidized active center. Based on our findings, two higher O2-tolerant KHyd3 mutations G300E and G300M were developed.

Hydrogen production by Rhodobacter sphaeroides DSM 158 under intense irradiation

To identify optimal hydrogen production conditions using growing cultures of Rhodobacter sphaeroides DSM 158 the effects of varying the reactor's volumetric power input (0.01-1.4kWm(-3)) and irradiation intensity (5-2500Wm(-2)) were investigated in batch and continuous production modes. Irradiation intensity had a greater effect on hydrogen production than volumetric power input. Hydrogen production and photofermentative biomass formation were maximized by irradiation at 2250Wm(-2) with a volumetric power input of 0.55kWm(-3). The bacterial dry weight (2.64gL(-1)) and rate of hydrogen production (195mLL(-1)h(-1)) achieved under these conditions were greater than any that have previously been reported for batch-mode hydrogen production by R. sphaeroides. Continuous mode experiments (D=0.1h(-1)) yielded a bacterial dry weight, hydrogen production rate, productivity and hydrogen yield of 2.35±0.18gL(-1), 165±6.2mLL(-1)h(-1), 3.96LL(-1)d(-1) and 36.6%, respectively.